I have so much trouble figuring out this new AdMob. :-/

I've created a new House Ad Campaign. When I go to the Monetize button and select one of the apps in which the campaign runs, I have two Ad units available. One is for banner ads and other for interstitial ads. When editing banner mediation, everything is OK. I set the AdMob Network ads to 0.01 USD and House Ads to 0.02 USD. However, when editing Interstitial ads (I don't need it, since I run only banner house ads, but I wanted to see, what's in there), the AdMob network is disabled, while the House Ad campaign is set to 0.01 USD (even if I don't need interstitials).

Please see the screenshot here: Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

When testing my apps, the interstitial ads are show, even if they are supposedly disabled.

Does anyone understand this? Thanks.